The present invention relates to a device for supplying pressure to a piston actuator, which is provided for carrying out transmission shift functions. Pressure originating from an energy accumulator is supplied to the piston actuator via a valve device. A pressure regulating and/or control device is provided, by which the pressure with which the piston actuator is supplied can be regulated and/or controlled.
Devices are generally known, for example, from DE 102 49 341 DE and EP 1 067 319 B1. In DE 102 49 341 DE, in which the pressure regulation or control takes place as a function of stored control and/or regulating functions. According to EP 1 067 319 B1, it is additionally possible to incorporate the present position of the piston into the regulation or control.
It is possible, by way of the pressure regulation or control as a function of transmission parameters, to adapt the force used to actuate the actuating elements of the transmission to the present operating state of the transmission, and thereby to avoid an increased mechanical loading.
In the transmission actuator concept known from DE 33 15 221 C2, the actuation of the piston adjuster takes place, in contrast, with a constant pressure, which is extracted from a compressed air reservoir. Actuating elements provided in the transmission are correspondingly moved with the force resulting from the constant pressure. Here, the pressure held in the reservoir must be selected such that a gearshift can reliably take place even under extreme operating states, for example at very low temperatures. If there are no extreme operating states present in which the actuating elements of the transmission must be moved with a high force, the constant pressure leads to an increased mechanical loading of the actuating elements of the transmission, which can, in particular, include shift forks and stops, and therefore lead to increased wear.
Although the pressure regulation or control as a function of transmission parameters, as explained in the introduction, reduces wear considerably, it is still possible overall for operating states to occur which lead to higher wear than would be necessary.
The present invention is, therefore, based on the object of developing a devices and method such that mechanical loading of the actuating elements of the transmission is reduced to the minimum required level.
This, and other, objects are achieved by a device for supplying a piston actuator, which is provided for carrying out transmission shift functions, with pressure originating from an energy accumulator and supplied to the piston actuator via a valve device. A pressure regulating and/or control device is provided, by which the pressure with which the piston actuator is supplied can be regulated and/or controlled. The pressure regulating and/or control device regulates and/or controls the pressure as a function of at least one of the following variables: (a) temperature, in particular the operating temperature of the transmission; (b) loading state of a motor vehicle to which the transmission is assigned; and (c) gradient of the underlying surface on which the vehicle to which the transmission is assigned is traveling.
Advantageous embodiments and refinements of the invention are described herein.
The device according to the invention provides a pressure regulating and/or control device that regulates and/or controls the pressure as a function of at least one of the following variables:                temperature, in particular the operating temperature of the transmission,        loading state of a motor vehicle to which the transmission is assigned, and        gradient of the underlying surface on which the vehicle to which the transmission is assigned is traveling.        
The adaptation of the shift forces to at least one, though preferably to all of the variables reduces the mechanical loading of the actuating elements of the transmission to the minimum required value in the respective operating state of the overall vehicle, thereby reducing wear. It is, for example, possible for high shift forces to be selected at low temperatures and for relatively low shift forces to be selected at normal operating temperatures. It is also possible to generate higher shift forces in the case of a fully-loaded vehicle than in the case of an empty or only lightly-loaded vehicle. It can, additionally or alternatively, be advantageous to generate higher shift forces when traveling up a gradient than when traveling down a gradient.
In a preferred embodiment of the invention, it is provided that the pressure regulating and/or control device includes a relay valve. A relay valve of this type is suitable for influencing a working pressure as a function of a control pressure, which is applied to the relay valve, for example in such a way that the working pressure corresponds to the control pressure.
In this context, it is preferably also provided that the relay valve has a control inlet to which can be supplied a control pressure which is set by way of a solenoid valve device. In the control section of the system, the pressure medium volume flow rate is relatively small, so that the solenoid valve device may be of relatively small and, therefore, cost-effective design.
Here, one preferred embodiment of the invention provides that the solenoid valve device is activated by an electronic control unit. The electronic control unit can, in particular, be an already-existing control unit whose functionality has been expanded to include the actuation of the solenoid valve device.
It is also preferable for the pressure regulating and/or control device to include a pressure sensor whose output signal is supplied to the electronic control unit. Here, the pressure sensor may advantageously measure the working pressure which is set by way of the relay valve and is used to actuate the piston actuator. By use of such an arrangement, it is possible to provide a bona fide pressure regulating circuit.
In preferred embodiments of the device according to the invention, it is also provided that the pressure regulating and/or control device is provided between the energy accumulator and the valve device. With regard to other devices described in the prior art, this novel arrangement of the pressure regulating and/or control device permits the use of the invention with relatively small changes to the system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.